Management of unauthorized user equipments in a femto base station environment

ABSTRACT

A method of managing registration requests from unauthorized user equipments in a cellular communications network includes monitoring such further registration requests and maintaining a count of the total number of registration requests from said user equipment. Based on the counted number of unsuccessful registration requests, different mechanisms can be used to reject the registration request.

This invention relates to a basestation for a cellular communicationssystem, and in particular to a method of preventing registrationproblems within that cellular communications system.

BACKGROUND

In recent times, the use of femtocell basestations has been proposed,for use in cellular communications networks. Such femtocell basestationsmay typically be purchased by a user for use in an office or home, wherethey can be connected to a core network through the internet.Thereafter, the femtocell basestations act as regular basestationswithin the cellular network, and provide service for mobile phones (UEs)within that office or home.

Femtocells typically have a restricted number of dedicated(pre-provisioned) users to which they individually provide service.Local Access Control procedures in the femtocell restrict service toonly those users that are provisioned/authorised on that femtocell.

Mobiles (referred to as UEs henceforth) are able to discern whether theycan access any cell based on PLMN codes (from their home PLMN or otherpermitted/equivalent PLMN). However, for cells within the allowed PLMNcode(s), UEs are typically unable to ascertain which femtocells theywill or will not be granted service on. Therefore UEs will typicallyattempt to register for service on any otherwise suitable femtocell.

The “Home” femtocell(s) (defined as one or more cells where that UE isspecifically provisioned for service) will accept the registration andprovide service. However any “visited” femtocell (defined as any cellwhere the UE is not provisioned for service) will reject theregistration attempt.

This restricted number of authorized users leads to many problems thatare not typically encountered with conventional basestations within thecellular network.

STATEMENT OF INVENTION

According to the present invention, there is provided a method ofmanaging user equipments in a cellular communications network, themethod comprising:

-   -   at a basestation, receiving a registration request from a user        equipment which is unauthorized on said basestation;    -   monitoring for further registration requests from said user        equipment; and    -   maintaining a first count of the total number of registration        requests from said user equipment.

This has the advantage that the counted number of registration requestscan be used to determine a mechanism for rejecting further registrationrequests, in a manner that reduces negative impacts on the userequipment and on the network.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the following drawings, in which:

FIG. 1 is a block schematic diagram, illustrating a part of a cellularwireless communications network in accordance with an aspect of thepresent invention;

FIG. 2 illustrates an aspect of the system in accordance with theinvention.

FIG. 3 illustrates a further aspect of the system in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a part of a cellular wireless communications networkin accordance with an aspect of the present invention. Specifically,FIG. 1 shows a core network (CN) 10 and a radio network (RN) 12 of acellular wireless communications network. These are generallyconventional, and are illustrated and described herein only to thelimited extent necessary for an understanding of the present invention.

Thus, the core network 10 has connections into the Public SwitchedTelephone Network (PSTN) (not shown) and into a packet data network, forexample the internet 14. The radio network 12 may include, for example,a GSM radio network and/or a UMTS radio network, which are thengenerally conventional. As shown in FIG. 1, the radio network 12 has anumber of basestations (BS) 16 a, 16 b, 16 c connected thereto.

As will be recognized by the person skilled in the art, a typical radionetwork 12 will have many such basestations connected thereto. Thesebasestations provide coverage over respective geographic areas, orcells, such that a service is available to subscribers. Often, there isa group of basestations that together provide coverage to the whole ofthe intended service area, while other basestations provide additionalcoverage to smaller areas within that intended service area, inparticular to smaller areas where there is expected to be more demandfor the service. The cells served by the basestations of the first groupare then referred to as macrocells, while the smaller areas served bythe additional basestations are referred to as femtocells.

FIG. 1 also shows an additional basestation 18 that can be used toprovide coverage over a very small area, for example within a singlehome or office building. This is referred to as a femtocell basestation(FBS). The femtocell basestation 18 is available for purchase by acustomer from a general retail outlet and, after purchase, can beconnected into the mobile network operator's core network 10 over theinternet 14, by means of the customer's existing broadband internetconnection 20. Thus, a user of a conventional mobile phone 22 canestablish a connection through the femtocell basestation 18 with anotherdevice, in the same way that any other mobile phone can establish aconnection through one of the other basestations of the mobile networkoperator's network, such as the basestations 16 a, 16 b, 16 c.

As shown in FIG. 1, the core network 10 includes a management system(MS) 11, which is provided specifically for managing the femtocellbasestation 18 and the other femtocell basestations that are active inthe network.

As mentioned above, the macrocell basestations provide coverage to thewhole of the intended service area including the location of thefemtocell basestation 18 and the location of the mobile phone 22 whileit is in the coverage area of the femtocell basestation 18.

Where the femtocell basestation forms part of a UMTS network, a visitedfemtocell has numerous options (e.g. using certain “reject causes”)defined in the 3GPP standard on how to reject unauthorized UEs.Depending on the reject response, the following two undesiredconsequences of rejection may occur:

“Registration Reject Loop”: Where a rejected UE may back off for adefined period and then repeat the registration attempt again. Since thevisited cell will again reject the request (if using the same/similarreject response), the UE may enter into a continual cycle or “rejectionloop” (registration request>reject>request>reject> . . . etc). In theUE, such a cycle will cause undesirably fast battery drain. In thefemtocell basestation, a rejection loop will cause undesirable signalloading, diverting resources away from authorized users. This in turnmay lead to increased delays and capacity and performance restrictions.

“Home Lock-out”: In order to prevent further failed registrationattempts in a rejection loop, described above, a basestation may bar aUE from subsequent access to the femtocell by placing the location areacode (LAC) of that femtocell into a “forbidden” list for the UE. The UEwill then be blocked from accessing any other femtocell that happens toshare the same LAC. This can lead to an undesired “lock-out” situationon the UE's home femtocell(s) if they happen to have the same LAC thathas just been forbidden. When roaming back to the home cell(s) the UEwill not even attempt to request service.

The likelihood of undesired “home lock-out” is inversely proportional tothe size of the range of LAC codes used in the femtocell network. Whilea large LAC range, with each femtocell having a unique LAC code, isideal, this is not possible since:

a) The maximum LAC range is finite (approx 65K values) according to 3GPPstandards; and

b) The network operator may have preferences/constraints in their corenetwork which reduce this significantly further (e.g. perhaps to severalthousand values only).

The present invention is therefore aimed at minimizing reject loops andhome lock-out. As stated above, the number of LACs available to afemtocell basestation is finite. According to one aspect of the presentinvention, the allocation of LACs to femtocell basestations is managedto minimize the problem of home lock-out. On powering up, each femtocellbasestation selects its LAC from a defined range of LACs. Allocating arelatively large range of LACs from which to choose a LAC valueminimizes the chances of home lock-out, as re-use of LACs will be low.Allocating a small range of LACs increases the chances of home lock-out,as re-use will be high. The range of LACs allocated to the femtocellbasestation may vary depending on a number of factors.

Within the management system 11, then, the available LACs are dividedinto groups, and each femtocell basestation selects its own LAC from theappropriate group. For example, each femtocell basestation may randomlyselect an LAC from the appropriate group, but may also continue to usethe selected LAC only if no other nearby femtocell basestation is alsousing the same LAC. The femtocell basestation may learn of the LACs ofneighbouring basestations for example by detecting the signals of thosebasestations directly, or through communications with the managementsystem 11. In order to facilitate this latter technique, once thefemtocell basestation has chosen its LAC, it then informs the managementsystem 11 of the selected value. Neighbouring femtocells typically havedifferent LACs in order that a roaming UE can detect when it has movedinto the coverage of a different femtocell.

Each femtocell basestation may be categorized according to its intendeduse or deployment scenario. For example, a basestation in the “Home”category may have fewer authorized UEs, and so may require lower powerlevels than a basestation in the “Business” category. Further, abasestation in the “Public access” category is intended to be used byany passing UE, and therefore does not have a list of authorized users.A basestation may be in the “troublespot” category due to repeatedfailed access attempts by unauthorized users (for more details on thiscategory, see below). Many different categories may be thought of by oneskilled in the art. Defining the types of categories is essentially atask for the designer of the individual system, and the list ofcategories presented herein is not intended to be exhaustive or limitingon the scope of the invention in any way.

According to the present invention, public access femtocellbasestations, for example, may be allocated a smaller range of theavailable LACs. A public access basestation is designed for use by anyUE, and so will not reject a UE by placing its LAC on a forbidden list(or indeed may not reject a UE at all). Therefore, the problems ofreject loop and home lock-out do not typically occur in publicfemtocells.

The network of femtocell basestations may be such that there are morebusiness basestations than home basestations. In this scenario, the homebasestations may be allocated fewer LACs to select from, in order toactively manage the limited number of LACs available.

“Troublespot” femtocell basestations may be allocated a high number ofLACs, as it is likely that these basestations will reject UEs byforbidding the UE from accessing its LAC, potentially causing homelock-out. In a preferred embodiment, each basestation in the“troublespot” category may be allocated a unique LAC from a range ofLACs set aside for that purpose, so that home lock-out will not occur.Thus, if a basestation in this category selects a particular LAC, themanagement system 11 must verify that no other basestation has selectedthe same LAC.

Further, each femtocell basestation may monitor the surrounding RFenvironment to detect the presence of neighbouring macrocellbasestations. For example, if there is an adequate signal level from atleast one macrocell basestation, or “macro signal”, the problems ofregistration reject loop and home lock-out may occur less frequently: aUE which is rejected by the femtocell basestation may have a higherchance of success in registering with the surrounding macrocellbasestation, and so may be less ikely to repeatedly attempt registrationwith the femtocell. Conversely, if the macro signal is weak, rejectloops are more likely to occur, as the UE has fewer options to choosefrom when attempting to access the network.

Therefore, according to the present invention, the femtocell basestationmay also select its LAC from a group of LACs, with the choice of groupbeing based on the surrounding macro signal. A relatively small range ofLACs may be allocated to basestations that can detect an adequate macrosignal, as the likelihood of reject loops (and therefore home lock-out)in this instance is low. A larger range of LACs may be allocated tofemtocell basestations that can detect only a poor macro signal, or nomacro signal at all, as the likelihood of reject loops (and thereforehome lock-out) in this instance is high.

Further, the management system 11 may set a parameter within eachfemtocell basestation, setting the basis on which it can select its LAC.For example, the LAC may be selected whenever the device is powered up,and the parameter may allow the selection on a “fixed” basis, a“restore” basis, or a “random” basis.

Using the “fixed” basis, the management system 11 may in fact inform thefemtocell basestation explicitly which LAC to select. Using the“restore” basis, the femtocell basestation may simply reselect the LACthat it was using before it was powered down, provided that this is notfound to clash with the LAC of a neighbouring femtocell basestation.Using the “random” basis, the femtocell basestation may randomly selectany LAC different from the LAC that it was using before it was powereddown. By appropriate selection of the basis on which the LAC is to beselected, the risk of a home lock-out can be reduced still further.

As mentioned above, when a UE attempts to access a femtocell basestationon which it is not authorized, the basestation has a number of possibleresponses with which to reject the UE. The main rejection mechanisms areoutlined below:

Reject Using Reject Causes #12, #13 or #15: “Location Area not Allowed”

This adds the location area identity (LAI) value into the UE's forbiddenLAI list, and the UE will cease making further location registrationattempts immediately. This incurs risk of “home lock-out” and maytherefore be used selectively and in a controlled manner.

Reject Using Reject Cause: “Retry Upon Entry into a New Cell”

UEs will typically treat this as an abnormal rejection method and remainin the reject loop. However, in the future, it is anticipated that moreUEs will actually adopt the intended action and cease making furtherlocation registration attempts.

Early RR Signalling Abort

Once the femtocell detects that an unprovisioned UE has entered a rejectloop, the femtocell intentionally rejects subsequent RRC connectionrequests from that UE (unless for an emergency call). While the UE willremain in the reject loop, this has the benefit that the femtocell willnot waste RRC resources on the unprovisioned UE.

Accept Registration but Limit Service to Emergency Calls Only

Once the femtocell detects that an unprovisioned UE has entered a rejectloop, it will:

-   -   1. Accept the registration request.    -   2. Indicate this emergency service limitation to the user. There        are numerous options to achieve this; however, an example of one        method to achieve this is:        -   a. Femtocell sends MM-INFORMATION messages to the UE after            each Location Update procedure, using text string such as            “Emergency Access Only” in the network name field of the            MM-INFORMATION message.        -   b. The UE displays this text on the screen (in place of the            network name text).    -   3. The femtocell denies subsequent service requests from this        unprovisioned UE for all except emergency calls.

Note: Since support of MM-INFORMATION messages by UEs is optional, thismethod cannot be relied upon for all UEs.

According to the present invention, to confirm the persistence of a UEin the reject loop and avoid taking unnecessary action for UEs that aretransitory in the cell, the femtocell may be configured by themanagement system to detect and report the following threshold events.

When the femtocell receives the first location update request from anunprovisioned UE, it will commence a monitoring period (with durationconfigurable by the management system), where it counts subsequentregistration attempts by that UE. If the count exceeds a first threshold(also configured by the management system) at the end of the monitoringperiod, the femtocell will provide a “reject loop indication”(containing that UE's identity) to the management system. If the countsubsequently exceeds a second, higher, threshold, a further message issent to the management system.

The femtocell basestation may also monitor in a general way for failedregistration attempts. This extends the above monitoring and detectionmechanism to identify the scenario where the combined effect of multipletransitory UEs in reject loops is also highlighted, even though anyindividual UE may not trigger a reject loop indication itself. Thus thebasestation may keep a count of the total number of failed registrationattempts from all UEs. This count is then compared to a “troublespot”threshold. The monitoring period and threshold count are configurable bythe management system and, when this threshold is exceeded, thefemtocell will provide a “troublespot indication” to the managementsystem.

According to the present invention, the femtocell basestation mayrespond differently to a registration attempt by an unauthorized UEaccording to whether or not the first reject loop threshold, or thetroublespot threshold, have been exceeded. That is, the femtocell maysend a different one of the four rejection messages identified aboveaccording to whether the registration attempt is the first registrationattempt by that UE, or the latest attempt in a reject loop.

According to another embodiment, the femtocell basestation may responddifferently according to its category as identified above, e.g. “home”,“business”, “public”, “troublespot”, or any one of a number of differentpossibilities. For example, a “public” basestation may typically haveall four possible rejection messages disallowed, as the intention isthat it should provide service for any UE that requests it.

According to another embodiment, the femtocell basestation may responddifferently according to the surrounding RF environment. That is, thebasestation will monitor the “macro signal” to determine whether thereis an adequate signal from neighbouring macrocell basestations. Thefemtocell basestation may then respond differently to an unauthorized UEin the presence of an adequate macro signal as compared to the absenceof a macro signal. For example, as mentioned above, in the presence ofan adequate macro signal reject loops are unlikely to occur. In thiscase, the reject message that places the LAI on the UE's forbidden listmay be disallowed, preventing home lock-out.

FIG. 2 shows one possible configuration of rejection mechanisms. Thus,in the example illustrated in FIG. 2, there are three categories ofbasestation, namely home/business (with this category being subdividedbased on whether or not the femtocell basestation can detect a signalfrom a macrocell basestation with an acceptable power level), public andtroublespot basestations. For one or more of the categories, therejection mechanism can also depend on whether the registration attemptin question is during the monitoring period (that is, during phase 1),or after the first threshold number of registration requests has beenexceeded (that is, during phase 2).

The table shown in FIG. 2 also shows the status of four possiblerejection mechanisms, namely the four rejection mechanisms described inmore detail above, that is: rejecting the request using the cause “retryupon entry to new cell”; providing emergency access only; rejecting therequest using a cause that results in a forbidden location areaindicator (or code); and rejecting the RRC connection request.

Thus, for any given phase and category in the table, the status in eachcell shows whether that mechanism is either:

Disallowed, meaning that the mechanism is never performed in thatphase/category combination, and furthermore the system cannot bereconfigured to enable it; or

Configurable, meaning that the mechanism may be enabled or disabledunder dynamic control from the management system 11, either on a per FBSbasis, or (more typically) set as a policy across the population ofFBSs.

For each mechanism that is configurable, its default status (eitherenabled or disabled), is shown in parentheses in the table of FIG. 2.The default status is the standard, or recommended, status of anyconfigurable mechanism, although it is permitted for a skilled operator,who understands and accepts the consequences, to alter the setting fromthe default.

Thus, each of these responses is chosen autonomously within thefemtocell basestation itself, possibly within limits set by the systemdesigners or by the mobile network operator, but with the intention thata single femtocell basestation design can allow different customizedbehaviours within different networks or at different locations. Thus, byresponding to the UE without recourse to the management system, thebasestation may reduce the workload of the management system and speedup the time required to resolve a problem.

However, as mentioned above, the basestation may also send an indicationto the management system that a “troublespot” threshold has beenexceeded, as a result of a large number of failed registration requestsfrom one or more UEs. If a troublespot indication is sent, themanagement system may re-categorize the basestation into the“troublespot” category. In a preferred embodiment, the management systemmay only re-categorize the basestation after a certain number oftroublespot indications have been received. In this way, the managementsystem may avoid re-categorizing basestations on the basis of anisolated group of failed registration attempts.

When the management system has re-categorized a basestation into the“troublespot” category, different rejection mechanisms apply, as shownin FIG. 2.

Also, when the basestation sends a message to the management systemindicating that the number of rejections of a particular mobile phonehas exceeded a threshold, the management system may send an instructionto the basestation on how to respond to that specific mobile phone inthe rejection loop state. On receipt of such an instruction, the FBSinfers that phases 1 and 2 are concluded (for that specific mobilephone), and that therefore the rules in the table are no longerapplicable to that mobile phone.

Thereafter, the basestation will follow diligently the instructions sentfrom the management system in respect of that specific mobile phone(without further reference to the ‘rules’ shown in the table of FIG. 2,it being noted that the action instructed by the management system maydiffer from the rules followed during phases 1 & 2).

For example, if a reject loop indication has been received by themanagement system, it may compare the LAC of the reporting femtocellwith the LAC(s) of the rejected UE's home femtocell(s). If there is noduplication or overlap, the management system may instruct the femtocellto issue a reject cause #12, 13 or 15, i.e. putting the LAC on theforbidden list of the UE, as there is no danger of causing a homelock-out in that instance. By contrast, if there is an overlap betweenthe LAC of the reporting femtocell and the home cell of the UE, themanagement system may prevent the femtocell issuing a rejection undercause #12, 13 or 15.

Thus, in this phase of operation, although it is the FBS that performsthe recovery action, it performs the action as instructed by themanagement system.

According to another aspect of the invention, the number of LACsavailable to the femtocell basestations may be artificially increased byuse of virtual mapping techniques.

As mentioned above, the number of LACs available to the femtocellbasestation is finite, and this may be further reduced by limitationsimposed by the core network. For example, there may be as few as 10 LACsallocated by the network provider to the femtocell network, or tofemtocells of a particular category since the LACs allocated to thefemtocell network may be pre-allocated to particular categories.

To overcome this problem, the network of femtocell basestations mapseach of the LACs allocated by the core network to a higher number ofvirtual LACs used within the femtocell network. By increasing the numberof LACs allocated to the femtocell network, the likelihood of homelock-out is greatly reduced, simply because the probability of therejecting basestation's LAC being the same as that of the UE's home cellis reduced.

FIG. 3 illustrates an example of this concept.

In the example shown, there are 10 LACs allocated in the core networkfor use in the femtocell network. Each of the 10 LACs is mapped in themanagement system to a thousand virtual LACs.

The virtual ranges are co-ordinated and pre-assigned by the femtocellmanagement system, using the set of LACs that are not used by the macronetwork. A typical macro network uses a few hundred LACs in a typicalcountry, and as there are approximately 65,000 LACs in total, there maybe up to 64,000 LACs available for use in the virtual ranges.

Thus, once the femtocell is configured to use a virtual LAC, it willbroadcast the virtual values on the radio interface (i.e. incommunications with UEs), and intercept and translate every signal toand from the core network that carries the original LAC.

Further, according to another embodiment, the femtocell determineswhether mapping is necessary by detecting the surrounding RFenvironment. For example, if there is an adequate macro signal, as hasbeen discussed before, reject loops are less likely to occur. In thiscase, then, the basestation may determine that it is unnecessary toincrease the number of LACs through mapping. Conversely, if the macrosignal is poor, mapping may be needed to reduce the risk of homelock-out.

According to a further preferred embodiment, the femtocell basestationdetermines whether mapping is necessary according to its category asdefined above. For example, a “public” femtocell basestation willtypically not require mapping, as it is programmed not to rejectregistration attempts from any UE (and thus home lock-out will notoccur).

According to a further embodiment, femtocell basestations in whichsignificant and persistent reject loop activity occurs may be allocateda unique virtual LAC from a reserved list maintained by the managementsystem. As there is only a limited number of LACs, such a list must bestrictly controlled and unique LACs allocated only in the worst-casescenario. For example, this solution may be applied to basestations inthe “troublespot” category, or even only the worst basestations withinthat category. By allocating a unique LAC to the basestation, the systemovercomes any chance of home lock-out, as the rejecting basestation'sLAC cannot possibly then match the UE's home cell LAC.

There are therefore described several methods for overcoming theproblems of reject loops and home lock-out in femtocell networks.

The invention claimed is:
 1. A method of operation of a basestation in acellular communications network, the method comprising: maintaining alist of user equipments that are authorized to use the basestation; inresponse to a first registration request received from a user equipmentthat is not authorized to use the basestation: starting a timer;starting a count of registration requests received from said userequipment that is not authorized to use the basestation; andtransmitting a first rejection message to said user equipment that isnot authorized to use the basestation, wherein said first rejectionmessage permits the user equipment to make further registration requeststo said basestation; and in response to a subsequent registrationrequest received from said user equipment that is not authorized to usethe basestation within a first monitoring period after starting thetimer: incrementing said count of registration requests received fromsaid user equipment that is not authorized to use the basestation, themethod further comprising, when said count of registration requestsreceived from said user equipment that is not authorized to use thebasestation reaches a predetermined threshold within the firstmonitoring period: transmitting a second rejection message to said userequipment that is not authorized to use the basestation, wherein saidsecond rejection message prevents the user equipment from making furtherregistration requests to said basestation.
 2. A method as claimed inclaim 1, wherein said second rejection message causes a location area ofsaid basestation to be identified by the user equipment as forbidden. 3.A method as claimed in claim 1, further comprising: receivingregistration requests from a plurality of user equipments that areunauthorized on said basestation; and maintaining a second count of thetotal number of registration requests from said plurality ofunauthorized user equipments.
 4. A method as claimed in claim 2, furthercomprising: receiving registration requests from a plurality of userequipments that are unauthorized on said basestation; and maintaining asecond count of the total number of registration requests from saidplurality of unauthorized user equipments.
 5. A method as claimed inclaim 3, further comprising: comparing said second count with a secondthreshold; and if said second count exceeds said second threshold withina second monitoring period, transmitting a report to a management systemof said network.
 6. A method as claimed in claim 4, further comprising:comparing said second count with a second threshold; and if said secondcount exceeds said second threshold within a second monitoring period,transmitting a report to a management system of said network.
 7. Abasestation in a cellular communications network, comprising: memory,and one or more processors, the one or more processors configured to:maintain a list of user equipments that are authorized to use thebasestation; in response to a first registration request received from auser equipment that is not authorized to use the basestation: start atimer; start a count of registration requests received from said userequipment that is not authorized to use the basestation; and transmit afirst rejection message to said user equipment that is not authorized touse the basestation, wherein said first rejection message permits theuser equipment to make further registration requests to saidbasestation; and in response to a subsequent registration requestreceived from said user equipment that is not authorized to use thebasestation within a first monitoring period after starting the timer:increment said count of registration requests received from said userequipment that is not authorized to use the basestation, the one or moreprocessors further configured to: when said count of registrationrequests received from said user equipment that is not authorized to usethe basestation reaches a predetermined threshold within the firstmonitoring period: transmit a second rejection message to said userequipment that is not authorized to use the basestation, wherein saidsecond rejection message prevents the user equipment from making furtherregistration requests to said basestation.
 8. A basestation as claimedin claim 7, wherein said second rejection message causes a location areaof said basestation to be identified by the user equipment as forbidden.9. A basestation as claimed in claim 7, wherein the one or moreprocessors are further configured to: receive registration requests froma plurality of user equipments that are unauthorized on saidbasestation; and maintain a second count of the total number ofregistration requests from said plurality of unauthorized userequipments.
 10. A basestation as claimed in claim 8, wherein the one ormore processors are further configured to: receive registration requestsfrom a plurality of user equipments that are unauthorized on saidbasestation; and maintain a second count of the total number ofregistration requests from said plurality of unauthorized userequipments.
 11. A basestation as claimed in claim 9, wherein the one ormore processors are further configured to: compare said second countwith a second threshold; and if said second count exceeds said secondthreshold within a second monitoring period, transmit a report to amanagement system of said network.
 12. A basestation as claimed in claim10, wherein the one or more processors are further configured to:compare said second count with a second threshold; and if said secondcount exceeds said second threshold within a second monitoring period,transmit a report to a management system of said network.